Loose engine mounts

We had a new propeller shaft, cutlass bearings and engine mounts installed on the starboard side of our GB 36 in November 2016. In April of this year we noticed that the engine had slid down on three of the mounts. It appeared the bottom nuts had become loose and vibrated their down the mounting bolts. We had the shop that did the original install inspect, realign the shaft and tighten the mounts. When we got the bill, we disputed the charges as we have never heard of engine mounts (especially recently installed ones) working their way loose in such a short period of time.

Are we correct about that? Would engine mounts work their way loose after 16 months?

Appreciate any feedback or advice anyone would like to share.

Thanks,

Hal & Daniele Collins

If you are comfortable posting it, I’d like to know which yard. I would say they were not properly torqued the first time.

And welcome to the forum.

I would rather not say for the moment and get unbiased feedback as to whether this is something that is normal or that we should have been watching for or expecting.

Thanks.

Properly installed nuts and bolts can work free if the vibration is abnormal.

That may become a point of contention.

But I have seen the top nuts become loose, but never the bottom ones because of the weight on them. Maybe one could, but 3 sounds unusual.

Welcome aboard. I have never seen that happen, not saying it could not happen but does seem unusual.

I have seen the bottom nuts down on quite a few boats over the years. In one case the engine was hobby horsing on the mounts. I ran the low nut up to the bottom of the mount while underway stopping the engine's extra motion. Still needed an alignment to be sure it was OK>

More recently a pair of engines that had recent alignments had loose jacking nuts on one side and considerable vibration the other. Realignment and tightening took care of the problem.

If the engine is not balance on all four mounts it can shake too. Like a wobbly table in a restaurant. The one that always spills your drinks.

Not enough information to assign blame but interesting it occurred soon after you had the work done.

Thank you everyone for your replys. Very helpful.

Ill add that I had this issue on a port mount. It happened twice and the nuts were well torqued both times. The solution for me was to use ss wire and twist tool. Go under the nut around the bolt twist with plenty of extra wire after the twist. Then wrap up over the nut back around the top and another twist on back side. This prevents the bolt from moving. Practice used as common safety nut wiring on airplanes is good enough for my boat - it hasn't budged in 4 years.